Modern automobiles may have up 70 (or even more) electronic control units (ECU) for controlling the operation of various subsystems. Such subsystems may be, inter alia, engine management system, transmission control system, airbags control system, antilock braking system, cruise control, steering assist systems, multimedia and navigation systems, central locking system, mirror adjustment, battery management system, recharging systems for hybrid/electric cars, etc. Some of these subsystems may operation independently from subsystems, but communication between the ECUs of different subsystems may be essential. The Controller Area Network (CAN) standard was devised for this purpose. Although, CAN was developed for the use in automobiles, a CAN bus may also be used as a fieldbus in general industrial environments. Generally, a CAN bus may be regarded as a two-wire bus system with differential signaling.
The CAN specification was initially published by the Robert Bosch GmbH and later standardized by the International Organization for Standardization (ISO) as CAN standard ISO 11898, which was later restructured into two parts: ISO 11898-1 covering the data link layer, and ISO 11898-2 covering the CAN physical layer for high-speed CAN.
To connect electronic circuits to a CAN bus specific integrated CAN transceiver circuits (transceiver ICs) have been developed. In various automotive and industrial applications relatively high electromagnetic compatibility (EMC) standards are to be complied with to keep electromagnetic emission and electromagnetic interferences (EMI) at a sufficiently low level. A circuit design, which ensures that the common mode voltage of the bus lines remains approximately constant, may help to reduce electromagnetic emissions in a lower frequency range (e.g. up to 100 MHz). To reduce the electromagnetic emissions at high frequencies (e.g. 100 MHz and more) common-mode chokes may be used.